Low viscosity adhesive compositions containing asymmetric radial polymers

ABSTRACT

A low viscosity adhesive composition which comprises: 
     (a) an asymmetric radial block copolymer of a vinyl aromatic hydrocarbon and at least one conjugated diene having from 3 to 6 polymer arms, which: 
     (i) contains from 33 to 85% by weight of polyvinyl aromatic hydrocarbon block/polydiene block copolymer arms and the balance polydiene homopolymer arms, 
     (ii) has vinyl aromatic hydrocarbon blocks with block molecular weights of from 8000 to 30,000, 
     (iii) has conjugated diene blocks in the copolymer arms with a molecular weight of at least 6000, and 
     (iv) has a polyvinyl aromatic hydrocarbon content of from 10 to 40% by weight; and 
     (b) from 20 to 400 parts per hundred parts of polymer of a tackifying resin. 
     The invention also encompasses the polymers used in the adhesive.

FIELD OF THE INVENTION

The invention described herein relates to adhesive compositions whichhave a low viscosity and can be applied to thin substrates and topolymers used in such compositions. More particularly, this inventionrelates to the use of particular low viscosity asymmetric radial blockcopolymers in adhesive formulations.

BACKGROUND OF THE INVENTION

Block copolymers have been employed in adhesive compositions for manyyears, primarily because of their high cohesive strengths and theirability to phase separate and form physical associations which act ascrosslinks which are normally formed by chemical vulcanization. Blockcopolymers such as those described in U.S. Pat. No. 3,239,478 are eitherlinear or radial or star styrene-butadiene or styrene-isoprene blockcopolymers. These polymers generally have high cohesive strength and canbe readily tackified to yield good adhesive properties.

The use of many of these polymers in certain applications is limitedbecause the viscosities of the polymers are too high. For instance,adhesive manufacturers would like to lower the application temperatureof hot melt adhesives in order to apply them to thinner substrates andto improve the melt stability of the adhesive. However, lowerapplication temperatures (less than 300° F.) result in unacceptably highadhesive melt viscosities so that common processing and applicationequipment cannot be used. The common solution to this problem has beento add diblock polymer or make the main polymer with a high percentageof uncoupled diblock arms. This lowers the viscosity but has theundesirable effect of lowering the tensile strengths of these polymersand adhesives produced with them have poor properties. U.S. Pat. No.4,391,949 suggested another approach whereby a star-shaped asymmetricblock copolymer having styrene-diene and diene homopolymer arms wasused. These star polymers generally have very high viscosities, i.e.40,000 to 100,000 cps in adhesive compositions containing 40% polymer byweight.

Thus, it can be seen that there is a need for polymers which can be usedto produce adhesives with a better balance of properties, e.g. to beable to retain good adhesive properties and have lower viscosities. Aswill be seen below, the present invention helps to satisfy that need.

SUMMARY OF THE INVENTION

The present invention provides a low viscosity adhesive compositionwhich is comprised of a tackifying resin and an asymmetric radial vinylaromatic hydrocarbon/conjugated diene block copolymer having from threeto six arms which:

i) contains from 33 to 85% by weight of polyvinyl aromatic hydrocarbonblock/conjugated diene block copolymer arms and the balance homopolymerarms,

ii) has vinyl aromatic hydrocarbon blocks with a molecular weight of8000 to 30,000,

iii) has conjugated diene blocks in the copolymer arms with a molecularweight of at least 6000, and

iv) has a polyvinyl aromatic hydrocarbon content of from 10 to 40% byweight.

The composition also preferably contains from 20 to 400 parts perhundred rubber (phr) of a compatible tackifying resin. Parts per hundredrubber is a commonly used means for describing the concentrations of thecomponents in adhesive and other formulations. The "rubber" is thepolymer and it is referred to that way because it has elastomericproperties. The preferred vinyl aromatic hydrocarbon is styrene and thepreferred dienes are isoprene and butadiene.

DESCRIPTION OF THE INVENTION

The block copolymers of the present invention have an idealizedstructure as follows:

    (A--B).sub.x --Y--(C).sub.z

The subscript x ranges from 2 to 4 and z ranges from 1 to 4 and x+zranges from 3 to 6 (these asymmetric radial block copolymers may havefrom 3 to 6 arms). The A blocks are polymer blocks of a vinyl aromatichydrocarbon. Preferably, the vinyl aromatic hydrocarbon is styrene.Other useful vinyl aromatic hydrocarbons include alphamethyl styrene,various alkyl-substituted styrenes, alkoxy-substituted styrenes, vinylnaphthalene, vinyl toluene and the like. The B and C blocks are polymerblocks of conjugated dienes. Preferred dienes include butadiene andisoprene. Other dienes may also be used, including piperylene,methylpentyldiene, phenylbutadiene, 3,4-dimethyl-1,3-hexadiene,4,5-diethyl-l,3-octadiene and the like, preferably those conjugateddienes containing 4 to 8 carbon atoms. The conjugated diene employed inthe B block may differ from that employed in the C block. Mixtures ofconjugated dienes may also be employed.

The Y moiety stands for the multifunctional coupling agent used herein.In general, any of the coupling agents known in the prior art to beuseful in forming a radial polymer by contacting the same with a livingpolymer may be used in both the method of this invention and theasymmetric radial polymers of this invention. In general, suitablecoupling agents will contain three or more functional groups which willreact with the living polymer at the metal-carbon bond. Suitablecoupling agents, then, include SiX₄, RSiX₃, HSiX₃, X₃ Si--SiX₃, X₃Si--(CH₂)_(x) --SiX₃, RX₂ Si--(CH₂)_(x) --SiX₂ R, RX₂ Si--(CH₂)_(x)--SiX₂ --(CH₂)_(x) --SiX₂ R, R₂ XSi--(CH₂)_(x) --SiX₂ R, and the like.In the foregoing formulae: each X may, independently, be fluorine,chlorine, bromine, iodine, alkoxide radicals, hydride and the like; R isa hydrocarbyl radical having from 1 to about 10 carbon atoms, preferablyfrom 1 to about 6 carbon atoms; and x is a whole number from 1 to about6. Particularly useful coupling agents to prepare four armed asymmetricradial polymers include the silicon tetrahalides such as silicontetrafluoride, silicon tetrachloride, silicon tetrabromide, and thelike, and the tetraalkoxysilanes such as tetramethoxysilane,tetraethoxysilane, tetrapropoxysilane, and the like. Particularly usefulcoupling agents for preparing 6 armed polymers include X₃ Si--(CH₂)_(n)--SiX₃ where n≧0 and X is halogen, alkoxy, hydride, includingbis-trimethoxy-silylethane, bis-trichlorosilylethane, and1,6-bis(trichlorosilyl)hexane. The preferred coupling agent to make 6armed polymers is bis-trichlorosilylethane because it gives the highestcoupling yield.

The letters x and z in the foregoing formula stand for the averagenumber of arms of each type in each polymer composition. In the polymersmade according to the present invention, x+z is 3 to 6. x and z areintegers when referring to a single polymer molecule. The polymercomposition may be comprised of predominantly one structure (i.e., thepredominant asymmetric species contains exactly x polyvinyl aromatichydrocarbon/conjugated diene block copolymer arms and y homopolymerarms) or it may comprise a mixture of asymmetric radial polymericspecies which, on average, contain x copolymer arms and y homopolymerarms. The exact polymer composition (i.e., whether it is composed ofpredominantly one structure or a mixture of species) may vary with thetotal number of arms, the coupling agent used, the polymer armcomposition, the ratio of different polymer arm types, and/or polymerarm molecular weight.

At the lower end of the 33 to 85% w block copolymer content range,asymmetric polymers with, on average, less than two copolymer arms willbe too weak to make an acceptable adhesive. If the polymer is at thehigh end of this range, it could have, on average, less than two blockcopolymer arms and have sufficient strength.

In general, the polymers of this invention may be prepared using any ofthe well known methods used for coupling radial polymers. These methodsare particularly suitable for the preparation of asymmetric radialpolymers from so-called "living" polymers containing a single terminalmetal ion. For example, suitable coupling methods are described in U.S.Pat. No. 4,096,203 and EP 0,314,256. These references are hereinincorporated by reference. A preferred process is one wherein thedifferent arms to be contained in the asymmetric radial polymer arecontacted sequentially with the coupling agent. Generally, the couplingsequence will be controlled by the relative number of each arm sought inthe final product with that polymer intended to provide the greaternumber of arms contacted with the coupling agent first and that polymerintended to provide the next greatest number of arms contacted with thecoupling agent second. Another preferred method involves the use of aprotected functional initiator.

As is well known in the prior art, "living" polymers are polymerscontaining at least one active group such as a metal atom bondeddirectly to a carbon atom. "Living" polymers are readily prepared viaanionic polymerization. Living polymers containing a single terminalgroup are, of course, well known in the prior art. Methods for preparingsuch polymers are taught, for example, in U.S. Pat. Nos. 3,150,209;3,496,154; 3,498,960; 4,145,298 and 4,238,202. Methods for preparingblock copolymers such as those preferred for use in the method of thepresent invention are also taught, for example, in U.S. Pat. Nos.3,231,635; 3,265,765 and 3,322,856. These patents are hereinincorporated by reference. When the polymer product is a random ortapered copolymer, the monomers are, generally, added at the same time,although the faster reacting monomer may be added slowly in some cases,while, when the product is a block copolymer, the monomer used to formthe separate blocks are added sequentially,

In general, the polymers useful as arms in both the method of thisinvention and the asymmetric radial polymer of this invention may beprepared by contacting the monomer or monomers with an organoalkalimetal compound in a suitable solvent at a temperature within the rangefrom -150° C. to 300° C., preferably at a temperature within the rangefrom 0° C. to 100° C. Particularly effective polymerization initiatorsare organolithium compounds having the general formula:

    RLi

wherein R is an aliphatic, cycloaliphatic, alkyl-substitutedcycloaliphatic, aromatic or alkyl-substituted aromatic hydrocarbonradical having from 1 to 20 carbon atoms.

Suitable solvents include those useful in the solution polymerization ofthe polymer and include aliphatic, cycloaliphatic, alkyl-substitutedcycloaliphatic, aromatic and alkyl-substituted aromatic hydrocarbons,ethers and mixtures thereof. Suitable solvents, then, include aliphatichydrocarbons such as butane, pentane, hexane, heptane and the like,cycloaliphatic hydrocarbons such as cyclohexane, cycloheptane and thelike, alkyl-substituted cycloaliphatic hydrocarbons such asmethylcyclohexane, methylcycloheptane and the like, aromatichydrocarbons such as benzene and the alkyl-substituted aromatichydrocarbons such as toluene, xylene and the like and ethers such astetrahydrofuran, diethylether, di-n-butyl ether and the like.

It is desirable that the polymers of the present invention contain from33 to 85% by weight of polyvinyl aromatic hydrocarbon block/polydieneblock copolymer arms (for convenience, these will hereinafter bereferred to as SI arms, with the S standing for styrene and the Istanding for isoprene; however, the following description is meant to beapplicable to polymers containing the other vinyl aromatic hydrocarbonsand dienes described above). If the SI arm content is less than 33%, thepolymer will be too weak and adhesive properties will be unacceptable.If the SI arm content is higher than 85%, then the polymer will only bemarginally effective in reducing the viscosity of the adhesiveformulation.

If the polystyrene block molecular weights are less than 8000, again thepolymer will be too weak and adhesive properties will be poor. If thepolystyrene block molecular weights are more than 30,000, then theviscosity will be very high. The polydiene block molecular weights inthe copolymer arms must be greater than 6000 in order to form effectivechain entanglements leading to elastomeric behavior. The overallmolecular weight of the polymer may vary over a wide range, i.e. from50,000 to 400,000. However, for any specified molecular weight andpolyvinyl aromatic hydrocarbon content (for convenience, this will bereferred to hereinafter as PSC-polystyrene content in % by weight), theasymmetric radial polymers described herein will exhibit a lowerviscosity than the corresponding linear polymers while retaining theadvantageous properties of the linear polymers in formulating adhesives.Corresponding symmetric radial polymers are too weak as shown below.

The molecular weights of the blocks and polymers referred to herein aredetermined as follows. Molecular weights of linear polymers orunassembled linear segments of polymers such as mono-, di-, triblock,etc., arms of radial polymers before coupling are conveniently measuredby Gel Permeation Chromatography (GPC), where the GPC system has beenappropriately calibrated. For anionically polymerized linear polymers,the polymer is essentially monodisperse and it is both convenient andadequately descriptive to report the "peak" molecular weight of thenarrow molecular weight distribution observed. The peak molecular weightis usually the molecular weight of the main species shown on thechromatograph. For materials to be used in the columns of the GPC,styrene-divinyl benzene gels or silica gels are commonly used and areexcellent materials. Tetrahydrofuran is an excellent solvent forpolymers of the type described herein. Ultraviolet or refractive indexdetectors may be used.

The PSC of these polymers is important because if it is too low, thestrength of the polymer will be insufficient and if it is too high, thepolymer will be stiff and not behave like an elastomer. It is preferredthat the PSC range from 10 to 40% by weight.

If desired, these block copolymers may be hydrogenated. Unhydrogenated,partially hydrogenated, and fully hydrogenated polymers are includedwithin the scope of this invention. Hydrogenation may be effectedselectively as disclosed in U.S. Pat. No. Re. 27,145 which is hereinincorporated by reference. The hydrogenation of these copolymers may becarried out by a variety of well established processes includinghydrogenation in the presence of such catalysts as Raney Nickel, nobelmetals such as platinum and the like, soluble transition metal catalystsand titanium catalysts as in U.S. Pat. No. 5,039,755 which is alsoincorporated by reference. The polymers may have different diene blocksand these diene blocks may be selectively hydrogenated as described inU.S. Pat. No. 5,229,464 which is also herein incorporated by reference.

It is common practice to add an adhesion promoting or tackifying resinthat is compatible with the polymer, generally from 20 to 400 parts perhundred parts of polymer. A common tackifying resin is a diene-olefincopolymer of piperylene and 2-methyl-2-butene having a softening pointof about 95° C. This resin is available commercially under the tradenameWingtack® 95 and is prepared by the cationic polymerization of 60%piperlene, 10% isoprene, 5% cyclo-pentadiene, 15% 2-methyl-2-butene andabout 10% dimer, as taught in U.S. Pat. No. 3,577,398. Other tackifyingresins may be employed wherein the resinous copolymer comprises 20-80weight percent of piperylene and 80-20 weight percent of2-methyl-2-butene. The resins normally have ring and ball softeningpoints as determined by ASTM method E28 between about 80° C. and 115° C.

Aromatic resins may also be employed as tackifying agents, provided thatthey are compatible with the particular polymer used in the formulation.Normally, these resins should also have ring and ball softening pointsbetween about 80° C. and 115° C. although mixtures of aromatic resinshaving high and low softening points may also be used. Useful resinsinclude coumarone-indene resins, polystyrene resins, vinyl toluene-alphamethylstyrene copolymers and polyindene resins.

Other adhesion promoting resins which are also useful in thecompositions of this invention include hydrogenated rosins, esters ofrosins, polyterpenes, terpenephenol resins and polymerized mixedolefins, lower softening point resins and liquid resins. An example of aliquid resin is Adtac® LV resin from Hercules. To obtain goodthermo-oxidative and color stability, it is preferred that thetackifying resin be a saturated resin, e.g., a hydrogenateddicyclopentadiene resin such as Escorez® 5000 series resin made by Exxonor a hydrogenated polystyrene or polyalphamethylstyrene resin such asRegalrez® resin made by Hercules. Softening points of solid resins maybe from about 40° C. to about 120° C. Liquid resins, i.e., softeningpoints less than room temperature, may be used as well as combinationsof solid and liquid resins. The amount of adhesion promoting resinemployed varies from 20 to 400 parts by weight per hundred parts rubber(phr), preferably between 20 to 350 phr, most preferably 50 to 300 phr.The selection of the particular tackifying agent is, in large part,dependent upon the specific polymer employed in the respective adhesivecomposition.

A composition of the instant invention may contain plasticizers, such asrubber extending plasticizers, or compounding oils or organic orinorganic pigments and dyes. Rubber compounding oils are well-known inthe art and include both high saturates content oils and naphthenicoils. Preferred plasticizers are highly saturated oils, e.g. Tufflo®6056 and 6204 oil made by Arco and naphthenic process oils, e.g.Shellflex® 371 oil made by Shell. The amounts of rubber compounding oilemployed in the invention composition can vary from 0 to 150 phr,preferably form 0 to 80 phr.

Optional components of the present invention are stabilizers whichinhibit or retard heat degradation, oxidation, skin formation and colorformation. Stabilizers are typically added to the commercially availablecompounds in order to protect the polymers against heat degradation andoxidation during the preparation, use and high temperature storage ofthe composition. Combinations of primary and secondary antioxidants arepreferred. Such combinations include sterically hindered phenolics withphosphites or thioethers, such as hydroxyphenylpropionates with arylphosphates or thioethers, or amino phenols with aryl phosphates.Specific examples of useful antioxidant combinations include3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate)methane (Irganox® 1010 fromCiba-Geigy) with tris(nonylphenyl)-phosphite (Polygard® HR fromUniroyal), Irganox® 1010 with bis(2,4-di-t-butyl)pentaerythritoldiphosphite (Ultranox® 626 from Borg-Warner).

All compositions based on the polymers of this invention will containsome combination of the various formulating ingredients disclosedherein. No definite rules can be offered about which ingredients will beused. The skilled formulator will choose particular types of ingredientsand adjust their concentrations to give exactly the combination ofproperties needed in the composition for any specific adhesive orsealant application. A formulator skilled in the art will see tremendousversatility in the asymmetric radial polymers of this invention toprepare adhesives and sealants having properties suitable for manydifferent applications.

The adhesive compositions of the present invention can be prepared byblending the components at an elevated temperature, preferably betweenabout 50° C. and about 200° C., until a homogeneous blend is obtained,usually less than three (3) hours. Various methods of blending are knownto the art and any method that produces a homogenous blend issatisfactory. The resultant compositions may then be used in a widevariety of applications. Alternatively, the ingredients may be blendedinto a solvent.

There are several advantages of using lower viscosity polymers inadhesives. First, the lower viscosity means that higher solids contentscan be tolerated in solvent based formulations. This will reduce thevolatile organic content of the formulation. The reduced viscosity of100% solids adhesive formulations allows for easier processing, lowerheating (energy) requirements, lower processing temperatures whichresults in less degradation of the polymer during processing and allowsthe formulation to be applied in thinner layers while avoiding theproblem of burn through.

These polymer are useful in a wide variety of adhesive applicationsincluding tapes, labels, diaper assembly, decals, bookbinding, andconstruction mastics. However, they are most useful in applicationswhere low viscosity is advantageous such as hot melt assembly adhesives.

EXAMPLES

In the following examples, polymers were synthesized by standard anionicpolymerization techniques under an inert nitrogen atmosphere usingsec-butyllithium in cyclohexane solution (12% w) as initiator.

Polymer 1:

An asymmetric radial polymer was prepared by polymerizing in a firstreactor 30.2 lb of styrene in 270.86 lb of cyclohexane solvent with 845mls of sec-butyllithium anionic polymerization initiator at 60° C. for10 half-lives. Following this polymerization, 105.34 lb of the livingpolystyryl lithium in cyclohexane was transferred to a reactorcontaining 203.45 lb of cyclohexane and 42 lb of isoprene was added andthe isoprene polymerized at 60° C. for at least 10 half lives. In aseparate reactor, 13.1 lb of isoprene in 74.22 lb of cyclohexane waspolymerized using 411 mls of sec-butyllithium at 60° C. for at least 10half lives. To this polyisoprene was added 41.3 g of1,2-bis(trichlorosilyl)ethane coupling agent and the mixture was reactedfor 45 min at 60° C. To this partially coupled intermediate was added263.27 lb of the solution of styrene-isoprene diblock copolymer incyclohexane and 48 mls of 1,2-dimethoxyethane. This mixture was reactedfor 60 min at 60° C. to achieve coupling of the remaining sites of thepartially coupled intermediate. Any remaining living polymer arms wereterminated by the addition of 23 mls of methanol, and the resultingpolymer was isolated by contacting the polymer solution with highpressure steam followed by removal of the solid polymer from the liquidphase. The product polymer was determined to have a polystyrenemolecular weight of 11,200 g/mole and a polyisoprene molecular weight of44,700 in the diblock copolymer arms and a homopolyisoprene armmolecular weight of 10,700 g/mole by gel permeation chromatography(GPC). The polystyrene content as determined by ¹ H NMR is 12.7% w.

Polymer 2:

An asymmetric radial polymer was prepared by polymerizing in a firstreactor 14.9 lb of styrene in 277 lb of cyclohexane solvent with 410 mlsof sec-butyllithium anionic polymerization initiator at 60° C. for 10half-lives. Following polymerization of the styrene, 58.8 lb of isoprenewas added and the isoprene polymerized at 70° C. for at least 10half-lives. In a separate reactor, 13.3 lb of isoprene in 149.54 lb ofcyclohexane was polymerized using 440 mls of sec-butyllithium at 60° C.for at least 10 half-lives. To this polyisoprene was added 43.3 g of1,2-bis(trichlorosilyl)ethane coupling agent and the mixture was reactedfor 60 min at 60° C. To this partially coupled intermediate was added187.66 lb of the solution of polystyrene-polyisoprene diblock copolymerin cyclohexane from the first reactor and 15.89 mls of1,2-dimethoxyethane. This mixture was reacted for 60 min at 60° C. toachieve coupling of the remaining sites of the partially coupledintermediate. Any remaining living polymer arms were terminated by theaddition of approximately 40 mls of methanol, and the resulting polymerwas isolated by contacting the polymer solution with high pressure steamfollowed by removal of the solid polymer from the liquid phase. Theproduct polymer was determined to have a polystyrene molecular weight of11,800 g/mole and a polyisoprene molecular weight of 48,000 in thediblock copolymer arms and a molecular weight of 11,600 g/mole of thehomopolyisoprene arms by gel permeation chromatography (GPC). Thepolystyrene content as determined by ¹ H NMR is 13.2% w.

Polymer 3, 4, 5, and 6:

Four asymmetric radial polymers were prepared in the same manner asExample 2 except for changes in the amount of solvent, reagents, andcoupling conditions used. Table 1 describes the polymerization andanalysis of these polymers.

                  TABLE 1                                                         ______________________________________                                               Polymer 3                                                                             Polymer 4 Polymer 5 Polymer 6                                  ______________________________________                                        First reactor                                                                 lbs of   280.56    276.84    280.4   80.1                                     cyclohexane                                                                   lbs of styrene                                                                         28.2      26.2      30.2    3.54                                     mls of sec-                                                                            590       810       680     106.35                                   butyllithium                                                                  lbs of   .sup. 42.sup.a                                                                          47.6      40      16.47                                    isoprene                                                                      Second                                                                        reactor                                                                       lbs of   221.09    273.02    346.24  55.65                                    cyclohexane                                                                   lbs of   42.8      48.6      61.4    1.41                                     isoprene                                                                      mls of sec-                                                                            800       610       700     84.87                                    butyllithium                                                                  First coupling                                                                step                                                                          g of 1,2-bis-                                                                          90        65        73      8.66                                     (trichloro-                                                                   silyl)ethane                                                                  coupling 60        60        60      60                                       temperature                                                                   (°C.)                                                                  coupling time                                                                          60        75        60      25                                       Second                                                                        coupling step                                                                 lbs of S-I in                                                                          236.33    179.17    143.18  47.25                                    cyclohexane                                                                   transferred                                                                   activator type                                                                         1,2-di-   α-di-                                                                             α-di-                                                                           1,2-di-                                           methoxy-  methoxy-  methoxy-                                                                              methoxy-                                          ethane    benzene   benzene ethane                                   mls of   81        70        63      32.36                                    activator                                                                     coupling 70        70        70      80                                       temperature                                                                   (°C.)                                                                  coupling time                                                                          24 hrs    3 hrs     3 hrs   75 min                                   mis of    0        35        38      15                                       Methanol                                                                      Polymer                                                                       character-                                                                    istics.sup.b                                                                  styrene block                                                                          14,800    10,600    14,400  12,000                                   MW                                                                            isoprene of                                                                            23,060    19,100    20,300  45,000                                   S-I arm MW                                                                    isoprene of I                                                                          16,300    25,900    28,600  9,900                                    arm MW                                                                        polystyrene                                                                            21.3      16.1      14.2    16                                       content                                                                       (% w)                                                                         ______________________________________                                         .sup.a In this example, following polymerization of the isoprene, 186.4 g     of butadiene was polymerized for 5 halflives to provide a small block of      polybutadiene on each polystyrenepolyisoprene diblock copolymer chain.        .sup.b Molecular weights determined by GPC. Polystyrene contents              determined by .sup.1 H NMR.                                              

Polymer 7:

An asymmetric radial polymer was prepared by polymerizing in a firstreactor 4.18 lb of styrene in 79.99 lb of cyclohexane solvent with120.17 mls of sec-butyllithium anionic polymerization initiator at 50°C. °C. for 10 half-lives. Following polymerization of the styrene, 16.8lb of butadiene was added and the butadiene polymerized at 70° C. for 15half-lives. In a separate reactor, 2.46 lb of isoprene in 59.8 lb ofcyclohexane was polymerized using 88.2 mls of sec-butyllithium at 80° C.for at least 10 half-lives. To this polyisoprene was added 9.0 g of1,2-bis(trichlorosilyl)ethane coupling agent and the mixture was reactedfor 55 minutes at 60° C. To this partially coupled intermediate wasadded 43.42 lb of the solution of polystyrene-polybutadiene diblockcopolymer in cyclohexane from the first reactor and 6 mls of1,2-dimethoxyethane. This mixture was reacted for 90 min at 70° C. toachieve coupling of the remaining sites of the partially coupledintermediate. Any remaining living polymer arms were terminated by theaddition of approximately 15 mls of methanol, and the resulting polymerwas isolated precipitation into isopropanol. The product polymer wasdetermined to have a polystyrene molecular weight of 10,800 g/mole and apolybutadiene molecular weight of 45,000 in the diblock copolymer armsand a molecular weight of 9,900 g/mole of the homopolyisoprene arms bygel permeation chromatography (GPC). The polystyrene content asdetermined by ¹ H NMR is 16% w.

Polymer 8:

An asymmetric radial polymer was prepared by polymerizing in firstreactor 4.63 lb of styrene in 79.98 lb of cyclohexane solvent with 31mls of sec-butyllithium anionic polymerization initiator at 35° C. for 9half-lives. Following polymerization of the styrene, 15.38 lb ofbutadiene was added and the butadiene polymerized at 70° C. for at least10 half-lives. In a separate reactor, 3.49 lb of butadiene in 63.99 lbof cyclohexane was polymerized using 29 mls of sec-butyllithium at 80°C. for at least 10 half-lives. To this polybutadiene was added 12.75 gof 1,2-bis(trichlorosilyl)ethane coupling agent and the mixture wasreacted for 30 min at 60° C. To this partially coupled intermediate wasadded 35.02 lb of the solution of polystyrene-polybutadiene diblockcopolymer in cyclohexane from the first reactor and 8 mls of1,2-dimethoxyethane. This mixture was reacted for least 90 min at 80° C.to achieve coupling of the remaining sites of the partially coupledintermediate. Any remaining living polymer arms were terminated by theaddition of approximately 15 mls of methanol, and the resulting polymerwas isolated by precipitation into isopropanol. The product polymer wasdetermined to have a polystyrene molecular weight of 11,000 g/mole and apolybutadiene molecular weight of 38,000 in the diblock copolymer armsand a molecular weight of 9200 g/mole of the homopolybutadiene arms bygel permeation chromatography (GPC). The polystyrene content asdetermined by ¹ H NMR is 16% w.

Polymer 9:

An asymmetric radial polymer was prepared by polymerizing in a firstreactor 24.8 lb of styrene in 242 lb of cyclohexane solvent containing21 lb of diethylether with 975 mls of sec-butyllithium anionicpolymerization initiator at 60° C. for 8 half-lives. Followingpolymerization of the styrene, 62.6 lb of butadiene was added and theisoprene polymerized at 60° C. for 10 half-lives. In a separate reactor38.6 lb of isoprene in 226.4 lb of cyclohexane was polymerized using 870mls of sec-butyllithium at 60° C. for 10 half-lives. Followingpolymerization of the isoprene, 2 lb of butadiene was polymerized for 8half-lives at 60° C. to provide a small butadiene block for improvedcoupling. To this living polymer was added 72 mls of tetramethoxysilanecoupling agent and the mixture was reacted for 30 min at 60° C. To thispartially coupled intermediate was added 285 lb of the solution ofpolystyrene-polybutadiene diblock copolymer in cyclohexane from thefirst reactor and 180 mls of 1,2-dimethoxyethane. This mixture wasreacted for 60 min at 80° C. to achieve coupling of the remaining sitesof the partially coupled intermediate. Any remaining living polymer armswere terminated by the addition of approximately 8 mls of methanol, andthe resulting polymer was isolated by precipitation into isopropanol.The product polymer was determined to have a polystyrene molecularweight of 9,700 g/mole and a polybutadiene molecular weight of 23,200 inthe diblock copolymer arms and a molecular weight of 16,300 g/mole ofthe homopolyisoprene arms by gel permeation chromatography (GPC). Thepolystyrene content as determined by ¹ H NMR is 18.5% w.

Polymer 10:

An asymmetric radial polymer was prepared by polymerizing in a firstreactor 6.28 lb of styrene in 170 lb of cyclohexane solvent with 210 mlsof sec-butyllithium anionic polymerization initiator at 60° C. for 10half-lives. Following polymerization of the styrene, 23.85 lb ofisoprene was added and the isoprene polymerized at 60° C. for at least10 half-lives. To this living polystyrene-polyisoprene diblock copolymerwas added 15 mls of methyltrichlorosilane coupling agent and the mixturewas reacted for 40 min at 60° C. In a separate reactor, 25.03 lb ofisoprene in 225.26 lb of cyclohexane was polymerized using 200 mls ofsec-butyllithium at 60° C. for at least 10 half-lives. 120.8 lb of thisliving polyisoprene in cyclohexane was added to the partially coupledintermediate in the first reactor. This mixture was reacted for 60 minat 70° C. to achieve coupling of the remaining site of the partiallycoupled intermediate. The resulting polymer was isolated by contactingthe polymer solution with high pressure steam followed by removal of thesolid polymer from the liquid phase. The product polymer was determinedto have a polystyrene molecular weight of 10,500 g/mole and apolyisoprene molecular weight of 39,900 in the diblock copolymer armsand a molecular weight of 39,700 g/mole of the homopolyisoprene arms bygel permeation chromatography (GPC). The polystyrene content asdetermined by ¹ H NMR is 15.3% w.

Polymer 11:

An asymmetric radial polymer was prepared by a two step coupling processin a single reactor system. First, 15.1 grams of isoprene waspolymerized in 549 grams of cyclohexane solvent with 1.2 mls ofsec-butyllithium anionic polymerization initiator at 60° C. for at least10 half-lives. To this polyisoprene was added 1.01 grams of1,2-bis(trichlorosilyl)ethane coupling agent (as a 5% solution incyclohexane) and the mixture was reacted for 15 min at 60° C. 9.6 gramsof styrene was added and polymerized with 0.7 mls of mls ofsec-butyllithium anionic polymerization initiator at 60° C. for at least10 half-lives. Following polymerization of the styrene, 35.8 grams ofisoprene was added and the isoprene polymerized at 60° C. for at least10 half-lives. 0.3 mls of 1,2-diethoxyethane was added and the mixtureof partially coupled intermediate and living polystyrene-polyisoprenepolymer was coupled at 80° C. for 60 min. Any remaining living polymerarms were terminated by the addition of 1 ml of methanol, and theresulting polymer was isolated by precipitation into isopropanol. Theproduct polymer was determined to have a polystyrene molecular weight of8,700 g/mole and a polyisoprene molecular weight of 42,000 in thediblock copolymer arms and a molecular weight of 10,200 g/mole of thehomopolyisoprene arms by gel permeation chromatography (GPC). Thepolystyrene content as determined by ¹ H NMR is 15.1% w.

Comparative Polymer 12:

A symmetric radial polymer having six identical polymer arms composed ofpolystyrene-polyisoprene diblock copolymer was prepared for comparisonto the asymmetric radial polymers of this invention. 8.7 g of Styrenewas polymerized in 540 g of cyclohexane solvent with 1.51 mls ofsec-butyllithium anionic polymerization initiator at 60° C. for 20minutes. Following this polymerization, 55 g of isoprene was added andthe isoprene polymerized at 60° C. for at 20 minutes. To this livingpolystyrene-polyisoprene block copolymer was added 93 mg of1,2-bis(trichlorosilyl)ethane coupling agent and 0.4 ml of1,2-diethoxyethane and the mixture was reacted for 60 min at 80° C. Anyremaining living polymer arms were terminated by the addition of 1 ml ofmethanol, and the resulting polymer was isolated by precipitation intoisopropanol. The product polymer was determined to have a polystyrenemolecular weight of 4,300 g/mole and a polyisoprene molecular weight of25,500 g/mole by gel permeation chromatography (GPC). The polymer iscomposed of 90% w 6-arm symmetric radial polymer--(SI)₆ --and 10% wuncoupled SI diblock copolymer. The polystyrene content as determined by¹ H NMR is 14.9% w.

Neat Polymer Properties:

Polymer solution viscosities were determined using a BrookfieldViscometer using a #21 spindle. Tensile properties were determined onspecimens cut from toluene cast plaques 0.03-0.06 inches thick.

Adhesive Preparation and Evaluation:

To prepare the following adhesive formulations, the ingredients weresolution blended in toluene and cast from this solution onto Mylar forpreparation of specimens for adhesive property testing. Final adhesivethickness after drying was about 0.0016 inches. To determine the meltviscosity of the adhesive formulations, either the toluene solvent wasevaporated from the solution, or a separate, identical formulation wasprepared without the solvent by batch mixing a melt in a Baker PerkinsHot Oil Mixer at 350° F. Melt viscosities were determined on aBrookfield Viscometer using a #29 spindle.

The SAFT (shear adhesion failure temperature) was measured by 1"×1"Mylar to Mylar lap joint with a 1 kg weight. SAFT measures thetemperature at which the lap shear assembly fails under load. RollingBall Tack (RBT) is the distance a steel ball rolls on the adhesive filmwith a standard initial velocity (Pressure Sensitive Tape Council TestNo. 6). Small numbers indicate aggressive tack. Holding Power (HP) isthe time required to pull a standard area (1/2 in.× 1/2 in.) of tapefrom a standard test surface (steel, Kraft paper) under a standard load(2 kg), in shear at 2° antipeel (Pressure Sensitive Tape Council MethodNo. 7). Long times indicate high adhesive strength. 180° peel wasdetermined by Pressure Sensitive Tape Council Method No. 1. Largenumbers indicate high strength when peeling a test tape from a steelsubstrate. Polyken probe tack (PPT) was determined by ASTM D-2979. Looptack (LT) was determined using TLMI loop tack tester. High numbers forPPT and LT indicate aggressive tack. In the following tables, (a) refersto adhesive failure and (c) refers to cohesive failure.

Adhesive formulations were prepared, as described above, using Polymers1, 2, and 10 with the following composition: 20% w asymmetric radialpolymer, 58% w synthetic C5 tackifying resin, 22% wparaffinic/naphthenic oil and 1% w phenolic antioxidant. Neat polymercharacteristics and adhesive properties are summarized in Table 2. Forcomparison, an identical formulation was prepared using a linear polymercontaining a mixture of polystyrene-polyisoprene-polystyrene triblockcopolymer and polystyrene-polyisoprene polyisoprene diblock copolymer.In all linear polymers in this and the following examples the molecularweight of the polyisoprene block of thepolystyrene-polyisoprene-polystyrene triblock copolymer is equal totwice the molecular weight of the polyisoprene block of thepolystyrene-polyisoprene diblock copolymer. Properties of the linearpolymer and its adhesive is given in Table 2.

                                      TABLE 2                                     __________________________________________________________________________                                            Linear                                                  Polymer 1                                                                            Polymer 2                                                                            Polymer 10                                                                            Polymer A                             __________________________________________________________________________    Polymer Characteristics                                                       % wt of diblock arms in asymmetric                                                               75     75     70     --                                    radial polymer                                                                % w coupled polymer in linear                                                                   --     --     --         62                                 polymer                                                                       Polystyrene molecular weight (g/                                                                11,500 11,800 10,500  10,900                                mole)                                                                         Polyisoprene molecular weight of                                                                44,700 48,000 39,900  69,000                                polystyrene-polyisoprene diblock co-                                          polymer (g/mole)                                                              Total polymer molecular weight (g/                                                              155,200                                                                              166,000                                                                              140,500 159,800                               mole)                                                                         Polystyrene content (% w)                                                                       12.7   13.2   14.9     14.8                                 Solution viscosity (cps) 25% solids in                                                          277    319    458     822.5                                 toluene, 25° C.                                                        Ultimate tensile strength of neat                                                               932    602    695     1590                                  polymer (psi)                                                                 Adhesive Properties                                                           RB Tack (cm)      0.9 ± 0.1                                                                          1.4 ± 0.4                                                                        0.85 ± 0.39                                                                         0.8 ± 0.1                         Polyken Probe (kg)                                                                              1.43 ± 0.15                                                                        1.27 ± 0.11                                                                      1.21 ± 0.23                                                                         1.16 ± 0.14                       Loop Tack (oz.)   101 ± 5 (c)                                                                       105 ± 6 (a)                                                                       75 ± 13                                                                            99.7 ± 3.8 (pc)                    1800 Peel (pli)   5.4 ± 0.1 (c)                                                                     11.7 ± 0.1 (c)                                                                    5.93 ± 0.78 (c)                                                                    6.45 ± 0.49 (c)                    HP/Steel (min)    14.2 ± 1.1 (c)                                                                    10.6 ± 5.0 (c)                                                                    7.25 ± 1.7 (c)                                                                     20.9 ± 0.9 (c)                     HP/Kraft (min)    0.8 ± 0.3 (a)                                                                     1.0 (c)                                                                              0.18 ± 0.03 (a)                                                                    1.75 ± 0.35 (a)                    SAFT/Mylar (°C.)                                                                         47 ± 7 (c)                                                                        50.8 ± 3.9 (c)                                                                    52 ± 2 (c)                                                                         48 ± 6 (pc)                        SAFT/KRAFT (°C.)                                                                         32 (a) 40.0 ± 4.2 (c)                                                                    32 ± 2 (a)                                                                         36 ± 0 (a)                         Melt Viscosity (cps), 350° F.                                                            580    595    663     1130                                  __________________________________________________________________________

From the data presented in Table 2, it is apparent that for adhesivecompositions of comparable properties, the polymers of this inventionhave both neat polymer solution viscosity and adhesive formulation meltviscosities which are much lower than that obtained using a linearpolymer. The polymers of this invention are much more effective inreducing adhesive composition viscosity than the prior art method ofdecreasing the amount of coupled liner polymer.

An adhesive formulation was prepared, as described above, using Polymer11 with the following composition: 20% w asymmetric radial polymer, 58%w synthetic C5 tackifying resin, 22% w paraffinic/naphthenic oil and 1%w phenolic antioxidant. Neat polymer characteristics and adhesiveproperties are summarized in Table 3. For comparison, an identicalformulation was prepared using a polymer containing a mixture of linearpolystyrene-polyisoprene-polystyrene triblock copolymer and linearpolystyrene-polyisoprene diblock copolymer. In addition, an identicaladhesive formulation was prepared using Polymer 12, a six-arm symmetricradial polymer containing polystyrene-polyisoprene arms prepared asdescribed above. Properties of the linear and symmetric radial polymersand their adhesives are given in Table 3.

                  TABLE 3                                                         ______________________________________                                                                      Radial                                                            Linear      Comparative                                             Polymer 11                                                                              Polymer B   Polymer 12                                      ______________________________________                                        Polymer                                                                       Characteristics                                                               % wt of diblock                                                                          75         --          --                                          arms in                                                                       asymmetric                                                                    radial polymer                                                                % w coupled                                                                             --           30          90                                         polymer in                                                                    linear polymer                                                                Polystyrene                                                                             8,700       10,800      4,300                                       MW (g/mole)                                                                   Polyisoprene                                                                            42,000      69,000      25,500                                      MW of poly-                                                                   styrene-                                                                      polyisoprene                                                                  block co-                                                                     polymer (g/                                                                   mole)                                                                         Total polymer                                                                           142,200     159,600     178,800                                     MW (g/mole)                                                                   Polystyrene                                                                             15.1        14.8        14.9                                        content (% w)                                                                 Solution  153         488         165                                         viscosity (cps)                                                               25% solids in                                                                 toluene, 25° C.                                                        Ultimate tensile                                                                        424         487          55                                         strength of neat                                                              polymer (psi)                                                                 Adhesive                                                                      Properties                                                                    RB Tack (cm)                                                                            0.8 ± 0.2                                                                              0.8 ± 0.1                                                                              17.1 ± 7.8                               Polyken Probe                                                                           1.23 ± 0.32                                                                            1.01 ± 0.23                                                                            1.62 ± .18                               (kg)                                                                          Loop Tack 118 ± 23 (c)                                                                           89 ± 4 (pc)                                                                            48 ± 6                                   (oz.)                                                                         180° Peel (pli)                                                                  4.25 ± 0.07 (c)                                                                        2.4 ± 0.7 (c)                                                                           3.44 ± 0.06                             HP/Steel (min)                                                                          1.6 ± 0.7 (c)                                                                          2.7 ± 0.7 (c)                                                                           1.68 ± 0.04                             HP/Kraft (min)                                                                          0.3 ± 0.04 (pc)                                                                        0.53 ± 0.04 (c)                                                                         0.4                                        SAFT/Mylar                                                                              34.8 ± 6.7 (c)                                                                         42.3 ± 3.9 (c)                                                                         35.9 ± 0.1                               (°C.)                                                                  SAFT/KRAFT                                                                              34 (c)      39.3 ± 0.4 (c)                                                                         30 ± 2.8                                 (°C.)                                                                  Melt Viscosity                                                                          350         670         380                                         (cps), 350° F.                                                         ______________________________________                                    

From the data presented in Table 3, it is apparent that for adhesivecompositions of comparable properties, the polymers of this inventionhave both neat polymer solution viscosity and adhesive formulation meltviscosities which are much lower than that obtained using a linearpolymer. The polymers of this invention are much more effective inreducing adhesive composition viscosity than the prior art method ofdecreasing the amount of coupled liner polymer. While the symmetricradial Polymer 12 does result in a very low adhesive formulation meltviscosity, the polymer has very low tensile strength and also producesan unacceptable adhesive, specifically providing poor rolling ball andloop tack.

An adhesive formulation was prepared, as described above, using Polymer4 with the composition shown in Table 4. Neat polymer characteristicsand adhesive properties are summarized in Table 4. For comparison,equivalent formulations were prepared using linear polymers containingof a mixture of polystyrene-polyisoprene-polystyrene triblock copolymerand polystyrene-polyisoprene diblock copolymer. Properties of theselinear polymers and compositions and properties of their adhesives aregiven in Table 4.

                                      TABLE 4                                     __________________________________________________________________________                             Linear Linear Linear                                                   Polymer 4                                                                            Polymer C                                                                            Polymer D                                                                            Polymer E                              __________________________________________________________________________    Polymer Characteristics                                                       % wt of diblock arms in asymmetric                                                              44     --     --     --                                     radial polymer                                                                % w coupled polymer in linear                                                                   --     23     14      0                                     polymer                                                                       Polystyrene MW (g/mole)                                                                         10,600 10,800 10,800 10,600                                 Polyisoprone MW in poly-                                                                        19,100 69,000 69,000 69,000                                 styrene-polyisoprene diblock                                                  copolymer (g/mole)                                                            Total polymer MW (g/mole)                                                                       163,000                                                                              159,600                                                                              159,600                                                                              159,600                                Polystyrene content (% w)                                                                       16.1   14.8   14.8   14.8                                   Solution viscosity (cps) 25% solids in                                                          115    378    259    199                                    toluene, 25° C.                                                        Ultimate tensile strength of neat                                                               67     226    82     10                                     polymer (psi)                                                                 Adhesive Properties                                                           % Polymer         50     50     50     50                                     % Synthetic C5 resin                                                                            49.5   50     50     50                                     % Paraffinic/Naphthenic Oil                                                                      0.5    0      0      0                                     % Phenolic Antioxidant                                                                           1      1      1      1                                     Adhesive Properties                                                           Polyken Probe (kg)                                                                               1.61   0.95   1.37   1.16                                  Loop Tack (oz.)   70     88     137    129                                    180° Peel (pli)                                                                          4.8 (c)                                                                              10 (c) 7.3 (c)                                                                              6.9 (c)                                HP/Steel (min)    27     860    39     4.1 (c)                                HP/Kraft (min)     3     14      5     0.4 (c)                                SAFT/Mylar (°C.)                                                                         70 (c) 73 (c) 70 (c)  53 (c)                                SAFT/KRAFT (°C.)                                                                         48 (c) 55 (a) 55 (a)  38 (c)                                Melt Viscosity (cps), 350° F.                                                            3,990  76,000 29,000 16,800                                 __________________________________________________________________________

From the data presented in Table 4, it is apparent that for adhesivecompositions of comparable properties, the polymers of this inventionhave both neat polymer solution viscosity and adhesive formulation meltviscosities which are much lower than that obtained using a linearpolymer. The polymers of this invention are much more effective inreducing adhesive composition viscosity than the prior art method ofdecreasing the amount of coupled liner polymer. Linear Polymer Eproduces an unacceptable adhesive which has poor cohesive strength,resulting in very poor holding power and SAFT performance.

Adhesive formulations were prepared, as described above, using Polymers3 and 5 with the compositions shown in Table 5. Neat polymercharacteristics and adhesive properties are summarized in Table 5. Forcomparison, an equivalent formulation was prepared using a linearpolymer containing of a mixture of polystyrene-polyisoprene-polystyrenetriblock copolymer and polystyrene-polyisoprene diblock copolymer.Properties of the linear polymer and composition and properties of itsadhesive are given in Table 5.

                  TABLE 5                                                         ______________________________________                                                                       Linear                                                     Polymer 3                                                                             Polymer 5  Polymer F                                      ______________________________________                                        Polymer Characteristics                                                       % wt SI arms in                                                                             52.5      32         --                                         asymmetric radial                                                             polymer                                                                       % w coupled polymer in                                                                      --        --          35                                        linear polymer                                                                Polystyrene MW (g/                                                                          14,800    14,400     15,500                                     mole)                                                                         Polyisoprene MW in                                                                          23,060    20,300     60,000                                     polystyrene-polyisoprene                                                      diblock copolymer (g/                                                         mole)                                                                         Total polymer MW (g/                                                                        140,920   183,800    151,000                                    mole)                                                                         Polystyrene content (%                                                                      21.3      14.2        22                                        w)                                                                            Solution viscosity (cps)                                                                    167       161        314                                        25% solids in toluene,                                                        25° C.                                                                 Ultimate tensile strength                                                                   167       21         237                                        (psi)                                                                         Adhesive Formulation                                                          % Polymer      50       50          50                                        % Synthetic C5 resin                                                                        48.5      50         48.5                                       % Paraffinic/Naphthenic                                                                     2.5        0         1.5                                        Oil                                                                           % Phenolic Antioxidant                                                                      .5        .5         .5                                         Adhesive Properties                                                           Polyken Probe (kg)                                                                          1.46      1.29       1.35                                       Loop Tack (oz.)                                                                              97       144        1.27                                       180° Peel (pli)                                                                      3.5 (c)    3 (c)     10 (c)                                     HP/Steel (min)                                                                              3900       8         965 (c)                                    HP/Kraft (min)                                                                              318        1         306                                        SAFT/Mylar (°C.)                                                                     80 (c)    32 (c)     90 (c)                                     SAFT/KRAFT (°C.)                                                                     72 (c)    39 (c)     75 (a)                                     Formulation Melt Vis-                                                                       334,500   94,500     >2 million                                 cosity 350° F. (cps)                                                   ______________________________________                                    

From the data presented in Table 5, it is apparent that for adhesivecompositions of comparable properties, the polymers of this inventionhave both neat polymer solution viscosity and adhesive formulation meltviscosities which are much lower than that obtained using a linearpolymer. The polymers of this invention are much more effective inreducing adhesive composition viscosity than the prior art method ofdecreasing the amount of coupled liner polymer. Polymer 5, whichcontains 32% w polystyrene-polyisoprene diblock copolymer arms, is veryeffective in reducing the adhesive melt viscosity, it produces anunacceptable adhesive which has poor cohesive strength, resulting invery poor holding power and SAFT performance. Thus, it is important thatthe asymmetric radial polymers of this invention contain at least 33% byweight of polystyrene-polydiene block copolymer arms.

Adhesive formulations were prepared, as described above, using Polymers1, 8, and 9 with the following composition: 20% w asymmetric radialpolymer, 58% w styrenated polyterpene tackifying resin, 22% wparaffinic/naphthenic oil and 1% w phenolic antioxidant. Neat polymercharacteristics and adhesive properties are summarized in Table 6. Forcomparison, an identical formulation was prepared using a linear polymercontaining a mixture of polystyrene-polybutadiene-polystyrene triblockcopolymer and polystyrene-polybutadiene diblock copolymer. Properties ofthe linear polymer and its adhesive are given in Table 6.

                                      TABLE 6                                     __________________________________________________________________________                                               Linear                                               Polymer 7                                                                              Polymer 8 Polymer 9                                                                           Polymer G                          __________________________________________________________________________    Polymer Characteristics                                                       % wt of diblock arms in asymmetric                                                               79       67        66   --                                 radial polymer                                                                % w coupled polymer in linear                                                                   --       --        --     50                                polymer                                                                       Polystyrene MW (g/mole)                                                                         10,800   11,000    9,700 11,000                             Polybutadiene MW in polystyrene-                                                                45,000   38,000    23,200                                                                              63,500                             polybutadiene diblock copolymer (g/                                           mole)                                                                         Total polymer MW (g/mole)                                                                       151,200  134,800   98,400                                                                              149,000                            Polystyrene content (% w)                                                                        16       16         18.4                                                                                 12.3                            Solution viscosity (cps) 25%                                                                    1263     996       216   6010                               solids in toluene, 25° C.                                              Ultimate tensile strength of neat                                                                764     450       221    999                               polymer (psi)                                                                 Adhesive Properties                                                           RB Tack (cm)      1.1 ± 0.2                                                                           0.9 ± 0.1                                                                            2.1 ± 0.5                                                                        0.8 ± 0.1                       Polyken Probe (kg)                                                                              1.34 ± 0.06                                                                         1.18 ± 0.19                                                                          1.81 ± 0.13                                                                      0.93 ± 0.11                     Loop Tack (oz.)   88 ± 0 (sl c)                                                                       107.5 ± 4.95 (pc)                                                                     119 ± 18.4                                                                      103.5 ± 20.5 (a)                180° Peel (pli)                                                                          6.55 ± 0.21 (c)                                                                     6.35 ± 0.07 (c)                                                                       5.5 ± 0.14                                                                      2.63 ± 0.04 (c)                 HP/Steel (min)    11.63 ± 3.15 (c)                                                                    3.2 ± 0.71 (c)                                                                       3.53 ± .011                                                                      8.73 ± 1.66 (c)                 HP/Kraft (min)    4.88 ± 0.18 (c)                                                                     2.23 ± 0.04 (e)                                                                      1.53 ± 0.18                                                                      4.03 ± 0.11 (c)                 SAFT/Mylar (°C.)                                                                         39.3 ± 0.4 (c)                                                                      38 ± 0 (c)                                                                           36.9 ± 0.14                                                                      32.5 ± 3.5 (c)                  SAFT/KRAFT (°C.)                                                                         36.5 ± 0.7 (c)                                                                      36.75 ± .35 (c)                                                                      35.5 ± 0.6                                                                       34 (c)                             Melt Viscosity (cps), 350° F.                                                            1320     1280      420   8130                               __________________________________________________________________________

From the data presented in Table 6, it is apparent that for adhesivecompositions of comparable properties, the polymers of this inventionhave both neat polymer solution viscosity and adhesive formulation meltviscosities which are much lower than that obtained using a linearpolymer. The polymers of this invention are much more effective inreducing adhesive composition viscosity than the prior art method ofdecreasing the amount of coupled liner polymer.

Two adhesive formulations were prepared, as described above, usingPolymer 1 with the following composition: 20% w asymmetric radialpolymer, 58% w hydrogenated hydrocarbon or styrenated polyterpenetackifying resin, 22% w paraffinic/naphthenic oil and 1% w phenolicantioxidant. Neat polymer characteristics and adhesive properties aresummarized in Table 7. For comparison, identical formulations wereprepared using a linear polymer containing a mixture ofpolystyrene-polyisoprene-polystyrene triblock copolymer andpolystyrene-polyisoprene diblock copolymer. Properties of the linearpolymer and its adhesives are given in Table 7.

                                      TABLE 7                                     __________________________________________________________________________                                          Linear                                                   Polymer 1                                                                            Polymer H                                                                            Polymer 1                                                                            Polymer H                               __________________________________________________________________________    Polymer Characteristics                                                       % wt of diblock copolymer arms in                                                              75     --     75     --                                      asymmetric radial polymer                                                     % w coupled polymer in linear                                                                  --     60     --     60                                      polymer                                                                       Polystyrene MW (g/mole)                                                                        11,200 10,600 11,200 10,600                                  Polyisoprene MW in polystyrene-                                                                44,700 52,500 44,700 52,500                                  polyisoprene diblock copolymer                                                (g/mole)                                                                      Polystyrene content (% w)                                                                      12.7   17.4   12.7   17.4                                    Total polymer MW (g/mole)                                                                      154,600                                                                              126,200                                                                              154,600                                                                              126,200                                 Solution viscosity (cps) 25% solids                                                            277    424    277    424                                     in toluene, 25° C.                                                     Ultimate tensile strength of neat                                                              932    657    932    657                                     polymer (psi)                                                                 Adhesive Formulation                                                          % Polymer        20     20     20     20                                      % Hydrogenated Hydrocarbon                                                                     58     58      0      0                                      Resin                                                                         % Styrenated Polyterpene Resin                                                                  0      0     58     58                                      % Paraffinic/Naphthenic Oil                                                                    22     22     22     22                                      % Phenolic Antioxidant                                                                         0.5    0.5    0.5    0.5                                     Melt Viscosity (cps)                                                          250° F.   9000   29,000 5510   9980                                    300° F.   3200   7800   1690   2340                                    350° F.   1400   3800   710    995                                     __________________________________________________________________________

The data presented in Table 7 shows that for adhesive compositions ofcomparable properties, the polymers of this invention give adhesiveformulation melt viscosities which are much lower than that obtainedusing a linear polymer when a variety of tackifying resins are employed.The polymers of this invention are much more effective in reducingadhesive composition viscosity than the prior art method of decreasingthe amount of coupled liner polymer. In addition, the difference inadhesive melt viscosity compared to identical formulations containinglinear polymers increases as temperature is decreased. The above meltviscosity versus temperature data fit an Arrhenius relationship andallow prediction of melt viscosities at different temperatures withinthe measured range. For the above formulations containing hydrogenatedhydrocarbon tackifying resin, at 292° F., Polymer 1 adhesive will havean equivalent viscosity to that which Linear Polymer H adhesive has at350° F. For the above formulations containing styrenated polyterpenetackifying resin, at 330° F., Polymer 1 adhesive will have an equivalentviscosity to that which Linear Polymer H adhesive has at 350° F. Thisillustrates that the low viscosity asymmetric radial polymers of thisinvention will allow for processing of adhesive formulations at lowertemperatures than linear polymers.

An adhesive formulation was prepared, as described above, using Polymer6 with the following composition: 20% w asymmetric radial polymer, 58% wsynthetic C5 tackifying resin, 22% w paraffinic/naphthenic oil and 1% wphenolic antioxidant. Neat polymer characteristics and adhesiveproperties are summarized in Table 8. For comparison, an identicalformulation was prepared using a linear polymer containing a mixture oflinear polystyrene-polyisoprene-polystyrene triblock copolymer andlinear polystyrene-polyisoprene diblock copolymer. Properties of thelinear polymer and its adhesive is given in Table 8.

                  TABLE 8                                                         ______________________________________                                                                  Linear                                                              Polymer 6 Polymer I                                           ______________________________________                                        Polymer Characteristics                                                       % wt of diblock arms in                                                                          86         --                                              asymmetric radial polymer                                                     % w coupled polymer in linear                                                                   --           84                                             polymer                                                                       Polystyrene MW (g/mole)                                                                         12,000      10,800                                          Polyisoprene MW in polystyrene-                                                                 45,000      69,000                                          polyisoprene diblock copolymer                                                (g/mole)                                                                      Total polymer MW (g/mole)                                                                       153,600     159,600                                         Polystyrene content (% w)                                                                        16         14.8                                            Solution viscosity (cps) 25%                                                                     708        1550                                            solids in toluene, 25° C.                                              Ultimate tensile strength of neat                                                               2140        2692                                            polymer (psi)                                                                 Adhesive Properties                                                           RB Tack (cm)      1.0 ± 0.2                                                                              0.8 ± 0.1                                    Polyken Probe (kg)                                                                              1.10 ± 0.09                                                                            1.20 ± 0.08                                  Loop Tack (oz.)   108.5 ± 3.5 (c)                                                                        88.5 ± 6.0 (a)                               180° Peel (pli)                                                                          14.8 ± 0.6 (c)                                                                         7.4 ± 0.6 (c)                                HP/Steel (min)    23.2 ± 5.7 (c)                                                                         23.6 ± 5.5 (c)                               HP/Kraft (min)    1.4 ± 0.6 (a)                                                                          1.3 ± 0.1 (a)                                SAFT/Mylar (°C.)                                                                         47.2 ± 1.6 (pc)                                                                        58 ± 3 (pc)                                  SAFT/KRAFT (°C.)                                                                         30.0 ± 3.5 (a)                                                                         34 ± 2 (a)                                   Melt Viscosity (cps), 350° F.                                                            1450        1630                                            ______________________________________                                    

From the data presented in Table 8, it is apparent that for adhesivecompositions of comparable properties, Polymer 6, which contains 86% wpolystyrene-polyisoprene diblock copolymer arms, is only marginallyeffective in reducing adhesive melt viscosity when compared to a linearpolymer. Thus, it is important that the asymmetric radial polymers ofthis invention contain 85% w or less styrene/isoprene block copolymerarms.

An adhesive formulation was prepared, as described above, using Polymer3 with the following composition: 25% w asymmetric radial polymer, 60% whydrogenated hydrocarbon tackifying resin, 15% w paraffinic/naphthenicoil and 0.5% w phenolic antioxidant. Neat polymer characteristics andadhesive properties are summarized in Table 9. For comparison, anidentical adhesive formulation was prepared using a linear polymercontaining a mixture of polystyrene-polyisoprene-polystyrene triblockcopolymer and polystyrene-polyisoprene diblock copolymer. Properties ofthe linear polymer and its adhesive are given in Table 9.

                  TABLE 9                                                         ______________________________________                                                                  Linear                                                               Polymer 3                                                                              Polymer J                                           ______________________________________                                        Polymer Characteristics                                                       % wt SI arms in Asymmetric                                                                       52.5       --                                              Radial Polymer                                                                % w Coupled Polymer in Linear                                                                    --         83                                              Polymer                                                                       Polystyrene MW (g/mole)                                                                          14,800     14,700                                          Polystyrene MW of polystyrene-                                                                   26,060     36,000                                          polyisoprene diblock copolymer                                                (g/mole)                                                                      Total Polymer MW (g/mole)                                                                        140,920    101,400                                         Polystyrene content (% w)                                                                        21.3       30                                              Solution viscosity (cps) 25% solids                                                              90         322                                             in toluene, 25° C.                                                     Ultimate tensile strength of neat                                                                290        2446                                            polymer (psi)                                                                 Adhesive Properties                                                           SAFT/Mylar (°C.)                                                                          67         74                                              Melt viscosity (cps) 350° F.                                                              860        2620                                            % loss in melt viscosity (cps)                                                                   33         59                                              350° F.                                                                after 48 hours at 350° F.                                              ______________________________________                                    

From the data presented in Table 9, it is apparent that for adhesivecompositions of comparable properties, the polymers of this inventionhave both neat polymer solution viscosity and adhesive formulation meltviscosities which are much lower than that obtained using a linearpolymer. The polymers of this invention are much more effective inreducing adhesive composition viscosity than the prior art method ofdecreasing the amount of coupled liner polymer. In addition, thepolymers of this invention also provide an improvement in the meltstability of the adhesive formulation after heat aging.

An adhesive formulation was prepared, as described above, using Polymer3 with the following composition: 34% w asymmetric radial polymer, 38% wsynthetic C5 tackifying resin, 28% w paraffinic/naphthenic oil and 1% wphenolic antioxidant. Neat polymer characteristics and adhesiveproperties are summarized in Table 10. For comparison, an identicaladhesive formulation was prepared using a linear polymer containing amixture of polystyrene-polyisoprene-polystyrene triblock copolymer andpolystyrene-polyisoprene diblock copolymer. Properties of the linearpolymer and its adhesive are given in Table 10.

                  TABLE 10                                                        ______________________________________                                                                   Linear                                                                Polymer 3                                                                             Polymer F                                          ______________________________________                                        Polymer Characteristics                                                       % wt Sl arms in Asymmetric Radial                                                                  52.5      --                                             Polymer                                                                       % w Coupled Polymer in Linear                                                                      --         35                                            Polymer                                                                       Polystyrene MW (g/mole)                                                                            14,800    15,500                                         Polyisoprene MW of polystyrene-                                                                    26,060    60,000                                         polyisoprene diblock copolymer (g/                                            mole)                                                                         Total Polymer MW (g/mole)                                                                          140,920   151,000                                        Polystyrene content (% w)                                                                          21.3       22                                            Solution viscosity (cps) 25% solids in                                                              90       314                                            toluene, 25° C.                                                        Ultimate tensile strength of neat                                                                  167       237                                            polymer (psi)                                                                 Adhesive Properties                                                           RB Tack (cm)         2.1       1.0                                            Polyken Probe (kg)   0.666     0.680                                          Loop Tack (oz.)       94c       63                                            180° Peel (pli)                                                                             2.6c      4.9c                                           HP/Steel (min)        8         18c                                           HP/Kraft (min)        2         1                                             SAFT/Mylar (°C.)                                                                             56        70                                            SAFT/KRAFT (°C.)                                                                             75c       58c                                           Melt Viscosity (cps), 350° F.                                                               6,000     29,000                                         Solution Viscosity in Cyclohexane at                                          25° C.                                                                 20% Polymer           85       257                                            25% Polymer          173       585                                            30% Polymer          514       2860                                           35% Polywr           3240      11,810                                         ______________________________________                                    

From the data presented in Table 10, it is apparent that for adhesivecompositions of comparable properties, the polymers of this inventionhave both neat polymer solution viscosity and adhesive formulation meltviscosities which are much lower than that obtained using a linearpolymer. The polymers of this invention are much more effective inreducing adhesive composition viscosity than the prior art method ofdecreasing the amount of coupled liner polymer. In addition, theasymmetric radial polymers of this invention show reduced solutionviscosity over a range of concentrations when compared to linearpolymers. This allows for the asymmetric radial polymers of thisinvention to be formulated into solution based adhesives at much higherconcentrations.

We claim:
 1. A low viscosity adhesive composition which comprises:(a) anasymmetric radial block copolymer of a vinyl aromatic hydrocarbon and atleast one conjugated diene having from 3 to 6 polymer arms, which:(i)contains from 40 to 80% by weight of polyvinyl aromatic hydrocarbonblock/polydiene block copolymer arms and the balance polydienehomopolymer arms, (ii) has vinyl aromatic hydrocarbon blocks with blockmolecular weights of from 8000 to 30,000, (iii) has conjugated dieneblocks in the copolymer arms with a molecular weight of at least 6000,and (iv) has a polyvinyl aromatic hydrocarbon content of from 10 to 40%by weight; and (b) from 20 to 400 parts per hundred parts of polymer ofa tackifying resin.
 2. The composition of claim 1 wherein the vinylaromatic hydrocarbon is styrene and the diene is isoprene or butadiene.3. The composition of claim 1 wherein the polymer has 4 arms.
 4. Thecomposition of claim 3 wherein the polymer has, on average, 2 copolymerarms and 2 homopolymer arms.